Polymer scale preventive agent, polymerization vessel for preventing polymer scale deposition, and process of producing polymer using said vessel

ABSTRACT

A polymer scale preventive agent for use in polymerization of a monomer having an ethylenically unsaturated double bond, comprising (A) a N-substituted leucophenothiazine having the general formula (I): ##STR1## wherein Z is a carbonyl group or a sulfonyl group, R 1 , R 2  and R 3  are a hydrogen atom, alkyl group, an amino group, etc., and (B) a water-soluble basic polysaccharide. The agent is used for forming a coating on the inner wall, etc. of a polymerization vessel. Deposition of polymer scale can be effectively prevented, and polymeric product with high whiteness is obtained.

This application is a division of application Ser. No. 07/883,345, filedon May 15, 1992, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a polymer scale preventive agent usefulin polymerization of a monomer having an ethylenically unsaturateddouble bond, a polymerization vessel for preventing polymer scaledeposition, and a process of producing polymer using said vessel.

2. Description of the Prior Art

In processes of preparing polymers by polymerizing a monomer in apolymerization vessel, the problem that polymer deposits on the innerwall surface and so forth in the form of scale, is known. The depositionof the polymer scale on the inner wall results in disadvantages that theyield of the polymer and cooling capacity of the polymerization vesselare lowered; that the polymer scale may peel and mix into manufacturedpolymer, thereby impairing the quality of the manufactured polymer; andthat removal of such polymer scale is laborious and hencetime-consuming. Further, since the polymer scale contains unreactedmonomer and operators may be exposed thereto, which may cause physicaldisorders in the operators.

Heretofore, as methods for preventing polymer scale deposition on theinner wall surface and so forth of a polymerization vessel inpolymerization of a monomer having an ethylenically unsaturated doublebond, methods in which substances exemplified below are coated on theinner wall surface, etc. as a scale preventive agent, have been known.

For example, particular polar organic compounds (Japanese PatentPublication (KOKOKU) No. 45-30343(1970)), a dye or pigment (JapanesePatent Publication (KOKOKU) No. 45-30835(1970), an aromatic aminecompound (Japanese Pre-examination Patent Publication (KOKAI) No.51-50887(1976)) and a reaction product of a phenolic compound and anaromatic aldehyde (Japanese Pre-examination Patent Publication (KOKAI)No. 55-54317(1980)) are disclosed.

In the meantime, vinyl chloride polymers obtained by polymerization arerequired to have a good whiteness. That is, when polymeric products suchas vinyl chloride polymers are formed or molded with no addition of acoloring agent, the resulting formed or molded product is colored moreor less. This coloration is called initial coloration, which is requiredto be as low as possible. Specifically, for example, the formed ormolded products are required to have an L value according to theHunter's color difference equation, which is described in JIS Z 8730(1980), of 70 or more.

The prior art polymer scale preventive agents generally include a greatnumber of colored substances as exemplified typically by the dyes andpigments described in Japanese Patent Publication (KOKOKU) Nos.45-30835(1970) and 52-24953(1977), the aromatic amine compoundsdescribed in Japanese Pre-examination Patent Publication (KOKAI) No.51-50887(1976), and the reaction products of a phenolic compound and anaromatic aldehyde described in Japanese Pre-examination PatentPublication (KOKAI) No. 55-54317(1980). Presumably, for this, a coloredpolymer is obtained in suspension polymerization and the like of vinylchloride, etc. in a polymerization vessel which has a coating comprisingthe polymer scale preventive agent described above formed on its innerwall. That is, according to measurement of the lightness L describedabove, the L may be measured to be 65 or less, and coloration is therebyconfirmed. Presumably, the coloration is caused by incorporation ofcomponents of the coating which has dissolved or peeled into thepolymerization mass. Improvement is required for producing a polymer ofhigh quality.

In the U.S. patent application Ser. No. 07/780,464 filed on Oct. 22,1991 by T. Shimizu et al., now abandoned, is disclosed a polymerpreventive agent, as one which is effective in producing polymericproducts with a low initial coloration, comprising an N-acylated orN-sulfonylated leucophenothiazine having the general formula: ##STR2##wherein Z is a carbonyl group or a sulfonyl group, R¹ and R² may be thesame or different and each represent a hydrogen atom, a hydroxyl groupor a group having the formula --N(R⁴)(R⁵) where R⁴ and R⁵ may be thesame or different and each represent a hydrogen atom, an alkyl group ora formyl group, and R³ is a hydrogen atom, halogen atom, alkyl group,haloalkyl group, alkoxyl group, aryl group or a group having theformula: --N(R⁶)(R⁷) where R⁶ and R⁷ may be the same or different andeach a hydrogen atom or an alkyl group. In the U.S. patent applicationSer. No. 07/705,554 filed on May 24, 1991 by T. Shimizu et al., now U.S.Pat. No. 5,153,281 is disclosed a polymer scale preventive agent, as onewhich is safe and effective in producing polymeric products with a lowinitial coloration, comprising a water-soluble basic polysaccharide suchas chitosans. The present invention relates to an improvement of theagents described in the U.S. applications above in prevention of polymerscale deposition.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a polymer scalepreventive agent which is capable of preventing polymer scale depositioneffectively, puts no color to polymeric product to thereby produce thepolymers with high whiteness, and are not poisonous and therefore causesno concern with respect to safety or sanitation, a polymerization vesselcapable of preventing polymer scale deposition using the same preventiveagent, and a process of producing a polymer using the polymerizationvessel.

Thus, the present invention provides, as a means of attaining saidobject, a polymer scale preventive agent for use in polymerization of amonomer having an ethylenically unsaturated double bond, comprising:

(A) an N-substituted leucophenothiazine having the general formula (I):##STR3## wherein Z is a carbonyl group or a sulfonyl group, R¹ and R²may be the same or different and each represent a hydrogen atom, ahydroxyl group or a group having the formula --N(R⁴)(R⁵) where R⁴ and R⁵may be the same or different and each represent a hydrogen atom, analkyl group or a formyl group, and R³ is a hydrogen atom, halogen atom,alkyl group, haloalkyl group, alkoxyl group, aryl group or a grouphaving the formula: --N(R⁶)(R⁷) where R⁶ and R⁷ may be the same ordifferent and each a hydrogen atom or an alkyl group, and

(B) a water-soluble basic polysaccharide.

Further the present invention provides a polymerization vessel having onits inner wall surfaces a coating for preventing deposition of polymerscale, wherein said coating comprises the components (A) and (B) above.

Furthermore, the present invention provides a process of producing apolymer by polymerization of a monomer having an ethylenicallyunsaturated double bond in a polymerization vessel, comprising the stepof carrying out said polymerization in said polymerization vessel havingon its inner surfaces said coating, wherein said coating comprises thecomponents (A) and (B), whereby the deposition of polymer scale isprevented.

According to the present invention, high whiteness polymers with an Lvalue of 70 or more can be prepared.

Further, according to the present invention, polymer scale depositioncan be effectively prevented, irrespectively of polymerizationconditions such as the kind of a monomer or a polymerization initiator,polymerization type, the kind of material constituting the inner wall ofpolymerization vessels, etc. That is, deposition of polymer scale can beeffectively prevented in polymerizations in which polymer scaledeposition has been difficult to prevent, e.g., in emulsionpolymerization, polymerizations using a polymerization vessel made ofstainless steel, or polymerizations using a polymerization initiatorwith a strong oxidative effect such as potassium peroxodisulfate and thelike.

Therefore, if polymerization is carried out under application of thepresent invention, the operation of removing polymer scale is notnecessarily conducted every polymerization run, thereby productivitybeing improved.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Polymer scale preventiveagent

(A) N-Substituted leucophenothiazine

The polymer scale preventive agent of the present invention comprises,as its essential component, an N-substituted leucophenothiazine havingthe general formula (I), including N-acylleucophenothiazine andN-sulfonylleucophenothiazine, which may be used singly or in combinationof the two.

In the general formula (I), preferred examples of the group --N(R⁴)(R⁵)include, for example, --NH₂, --N(CH₃)₂, --N(C₂ H₅)₂, --N(C₃ H₇)₂, --N(C₄H₉)₂ and --N(CH₃)₃ (CHO). R³ specifically represents a hydrogen atom, ahalogen atom such as Cl, Br I and F, an alkyl group such as methyl,ethyl, propyl and butyl, a haloalkyl group such as dichloromethyl, analkoxyl group such as methoxyl, ethoxyl, propoxyl and butoxy, and arylgroup such as phenyl, p-hydroxyphenyl, p-methoxyphenyl andp-chlorophenyl, and amino groups such as --NH₂, --NH(CH₃), --NH(C₂ H₅),--NH(C₃ H₇) and --NH(C₄ H₉).

The N-acylleucophenothiazine is represented by the general formula (II):##STR4## wherein R¹, R² and R³ are as defined above.

The N-acylleucophenothiazine can be obtained by reducing a phenothiazinecompound with hydrosulfite, allowing the resulting product to react withan acyl chloride in the presence of an alkali and washing the productwith a suitable solvent, followed by recrystallization.

The N-sulfonylleucophenothiazine is represented by the general formula(III): ##STR5## wherein R¹, R² and R³ are as defined above.

The N-sulfonylleucophenothiazine can be obtained by reducing aphenothiazine compound with hydrosulfite, allowing the resulting productto react with a sulfonyl chloride in the presence of an alkali andwashing the product with a suitable solvent, followed bycrystallization.

Among the N-substituted leucophenothiazines, particularly preferred areBenzoylmethylene Blue, Hydroxybenzoylmethylene Blue andSulfonylmethylene Blue.

The N-substituted leucophenothiazines may be used singly or incombination of two or more.

(B) Water-soluble basic polysaccharide

The water-soluble basic polysaccharide used in the present inventionincludes, for example, chitosans, water-soluble chitosan derivatives,polygalactosamines, water-soluble polygalactosamine derivatives andwater-soluble chitin derivatives.

Chitosans are a straight chain polysaccharide, i.e.,(poly-1,4-β-glucosamine), formed by polymerization through β-1,4 linkageof D-glucosamine. It can be obtained by deacetylization of chitincontained in the carapace of the Crustacea such as prawns, shrimps andcrabs. Recently a chitosan can be produced by culturing a mold, and thechitosan thus produced can be used in the same manner as those naturallyoccurring. The chitosans are insoluble in water under the neutralconditions, but soluble under the acidic conditions; hence the chitosansare used under a pH of less than 7.

The water-soluble chitosan derivatives which may be used in the presentinvention include the following:

(1) Organic acid salts and inorganic acid salts of chitosans. Theorganic acid specifically includes, for example, acetic acid, glycollicacid, malic acid, citric acid, and ascorbic acid. The inorganic acidincludes, for example, hydrochloric acid, sulfuric acid, nitric acid andphosphoric acid. Chitosans preferably have a deacetylization degree of40 to 100%.

(2) Water-soluble low molecular products obtained by decomposition ofchitosans, i.e., water-soluble glucosamine oligomers. Normally, 5 to20-mers of glucosamine are preferred. Such oligomers can be produced byconventional depolymerization methods, for example, the hydrochloricacid hydrolysis method (Japanese pre-examination patent publication(KOKAI) No. 61-21102(1986), the nitrate decomposition method (Japanesepre-examination patent publication (KOKAI) No. 62-184002(1987), thechlorine decomposition method (Japanese pre-examination patentpublication (KOKAI) No. 60-186504(1985), the phosphoric aciddecomposition method and decomposition methods using an enzyme ormicroorganism.

(3) Water-soluble derivatives of chitosans prepared by introducing ahydrophilic group thereinto. Examples are described in Japanesepre-examination patent publication (KOKAI) No. 63-14714(1988) andinclude polyoxyethylene chitosans, polyoxypropylene chitosans,phosphated chitosans, N-glycidyltrimethylammonium chitosans, anddihydropropylchitosans.

The polygalactosamines which may be used in the present invention areinsoluble in water under neutral conditions, but soluble under a pH of 7or less and therefore used under such conditions. Polygalactosamines canbe produced by culturing a mold (APPLICATION OF CHITIN AND CHITOSAN pp.24-26, Edited by Society for Research of Chitin and Chitosan, 1990,published by Giho-do Shuppan).

The water-soluble polygalactosamines include the following:

(1) Organic acid salts and inorganic acid salts of polygalactosaminesincluding salts of organic acids such as acetic acid, formic acid or thelike, and salts of inorganic acids such as hydrochloric acid, nitricacid or the like;

(2) Water-soluble low molecular products obtained by decomposition ofpolygalactosamines. Normally, 5 to 20-mers of galactosamine arepreferred. Such oligomers can be produced by decomposition methods usingan enzyme or microorganism.

The water-soluble chitin derivatives which may be used in the presentinvention, include the following:

(1) Water-soluble N-acetylglucosamine oligomers obtained bydecomposition of chitins. Normally, 5 to 20-mers are preferred. Sucholigomers can be produced by conventional depolymerization methods, forexample, the nitrous acid decomposition method, the formic aciddecomposition method, the chlorine decomposition method (Japanesepre-examination patent publication (KOKAI) No. 62-186504(1987)) ordecomposition methods using an enzyme (e.g., chittinase) or amicroorganism.

(2) Water-soluble derivatives of chitins prepared by introducing ahydrophilic group thereinto. Examples are described in Japanesepre-examination patent publication (KOKAI) No. 63-14714(1988) andinclude polyoxyethylene chitins, polyoxypropylene chitins, phosphatedchitins and dihydropropylchitins.

Among the water-soluble basic polysaccharides described above, preferredare the inorganic acid salts and organic acid salts of chitosans, havinga deacetylization degree of 65% or more and a viscosity at 20° C. in theform of an aqueous solution containing 0.5% by weight of the chitosanand 0.5% by weight of acetic acid of 30 cP or lower when measured with aB-type viscometer, and the organic or inorganic salts ofpolygalactosamines with a moleculare weight of 10,000 or more.

The water-soluble basic polysaccharides may be used singly or incombination of two or more.

The preferred combinations of the components (A) and (B) include thosespecifically described in Examples later.

According to the present invention, the use of the water-soluble basicpolysaccharide (B) in combination with the N-substitutedleucophenothiazine (A) provides a marked scale preventing effect even ifthe concentration of the latter is low. The mechanism of the action dueto the water-soluble basic polysaccharide is not clear. Presumably, theaction is caused because the water-soluble basic polysaccharide (B)affects the N-substituted leucophenothiazine (A), thereby increasing thehydrophilic nature thereof.

The amount of the water-soluble basic polysaccharide (B) in the polymerscale preventive agent of the present invention ranges normally from 0.1to 1,000 parts by weight, preferably 1 to 600 parts by weight, per 100parts by weight of the component (B). If the amount of the water-solublebasic polysaccharide (B) is too small or too large relative to thecomponent (A), improvement in scale preventing effect due to thecombined use of the components (A) and (B) is hardly obtained.

The polymer scale preventive agent of the present invention is used forpreventing polymer scale deposition on the inner wall surfaces, etc. ofa polymerization vessel, for example, by being used for forming acoating thereon.

The amount of the component (B) in the polymer scale preventive agent ofthe present invention ranges normally from 0.1 to 1,000 parts by weight,preferably 1 to 600 parts by weight, per 100 parts by weight of theamount of the component (A). If the amount of the water-soluble basicpolysaccharide (B) is too small or too large, improvement in scalepreventing effect due to the combined use of the components (A) and (B)is lowered.

The polymer scale preventive agent is used for forming a coating on theinner wall surfaces, and preferably the surfaces of parts with whichmonomer comes into contact during polymerization, e.g., a stirringshaft, stirring blades, baffles, condensing coils, etc. of apolymerization vessel, so that scale deposition in the vessel can beprevented. Normally, in forming said coating on the inner wall surfaces,etc. of a polymerization vessel, the polymer scale preventive agent isused in a liquid state, i.e., as a coating liquid.

Preparation of a coating liquid

The coating liquid mentioned above is prepared by dissolving ordispersing said components (A) and (B) in a solvent.

The solvents used for preparation of the coating solution include, forexample, water; alcohols such as methanol, ethanol, propanol, butanol,2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 3-methyl-1-butanol,2-methyl-2-butanol, 2-pentanol, etc.; ketones such as acetone, methylethyl ketone, methyl isobutyl ketone, etc.; esters such as methylformate, ethyl formate, methyl acetate, methyl acetoacetate, etc.;ethers such as 4-methyldioxolane, ethylene glycol diethyl ether, etc.;furans; and aprotic solvents such as dimethylformamide, dimethylsulfoxide, acetonitrile, etc. These solvents may be used singly or as amixed solvent of two or more thereof as appropriate.

The total concentration of the components (A) and (B) is not limited aslong as the coating weight described later can be obtained, and it isnormally in the range from 0.001 to 15% by weight, preferably from 0.01to 1% by weight.

To the coating liquid, for example, a cationic surfactant, a nonionicsurfactant, an anionic surfactant, and so forth can be added as long asthe scale preventing effect is not impaired.

Further, inorganic compounds can be added to the coating liquid suitablyas long as the low coloring property or the scale preventing effect isnot impaired. The inorganic compounds which may be added include, forexample, silicic acids or silicates such as orthosilicic acid,metasilicic acid, mesodisilicic acid, mesotrisilicic acid,mesotetrasilicic acid, sodium metasilicate, sodium orthosilicate, sodiumdisilicate, disilicate, sodium tetrasilicate and water glass; metallicsalts such as oxygen acid salts, acetates, nitrates, hydroxides orhalides of a metal selected from alkali earth metals such as magnesium,calcium, and barium, zinc family metals such as zinc, aluminum familymetals such as aluminum, and platinum family metals such as platinum;and inorganic colloids such as ferric hydroxide colloid, colloidalsilica, colloid of barium sulfate, and colloid of aluminum hydroxide.The above-mentioned inorganic colloids may be those prepared, forexample, by mechanical crushing, irradiation with ultrasonic wave,electrical dispersion or chemical methods.

Formation of coating

When the coating liquid prepared as described above is used for forminga coating on the inner wall surface of a polymerization vessel, first,the coating liquid is applied to the inner wall surface and then driedsufficiently, followed by washing with water if necessary. A coating isformed by these operations on the inner wall surface of thepolymerization vessel; hence the polymer scale deposition thereon can beprevented.

The above-mentioned coating is preferably formed on not only the innerwall surfaces of a polymerization vessel but also other parts with whichthe monomer comes into contact during polymerization. For example, it ispreferred to form the coating by applying said coating liquid on astirring shaft, stirring blades, condensers, headers, search coil,bolts, nuts, etc.

More preferably, the coating is formed on not only the parts with whichthe monomer comes into contact during polymerization but also otherparts on which polymer scale may deposit, for example, such as the innersurfaces of equipment and tubes of recovery system for unreactedmonomer. These parts, more specifically, are exemplified by the innerwall surfaces of monomer distillation columns, condensers, monomer stocktanks and valves, etc. in said recovery system.

The method of applying the coating liquid on the inner wall surface,etc. of a polymerization vessel is not particularly limited, andincludes, for example, the brush coating, spray coating, the method offiling the polymerization vessel, etc. with the coating liquid followedby withdrawal thereof, and automatic coating methods as disclosed inJapanese Pre-examination Patent Publication (KOKAI) Nos. 57-61001(1982)and 55-36288(1980), and Japanese Patent Publication (KOHYO) Nos.56-501116(1981) and 56-501117(1981), and Japanese Pre-examinationPublication (KOKAI) No. 59-11303(1984), etc.

The method of drying wet coated surface provided by application of thecoating liquid, is not limited, either. The drying is conductedpreferably at a temperature within the range from room temperature to100° C., typically 30° C. to 80°. Specifically, a method in which, afterthe liquid is applied, hot air with a suitable elevated temperature isblown to the coated surface, and a method in which the inner wallsurface of a polymerization vessel and the surfaces of other parts to becoated are previously heated at, e.g., 30°-80° C. and the coating liquidis directly applied to the heated surfaces, etc. After dried, the coatedsurfaces are washed with water if necessary.

The coating thus formed has normally a coating weight of 0.001 g/m² ormore, preferably from 0.05 to 2 g/m².

The above coating operation may be conducted every 1 to ten-odd batchesof polymerization. The formed coating has fairly good durability andretains the polymer scale-preventing action; therefore the coatingoperation is not necessarily performed for every batch ofpolymerization. Hence, the productivity of the manufactured polymer isimproved.

Polymerization

After forming the coating on the inner wall surfaces of a polymerizationvessel and other parts with which monomer may come into contact byapplication of the coating liquid, polymerization is carried out inaccordance with conventional procedures therein. That is, a monomerhaving an ethylenic double bond and a polymerization initiator(catalyst) are charged, and then, a polymerization medium such as water,etc. and, optionally, a dispersing agent such as suspension agents,solid dispersing agents, and nonionic and anionic emulsifying agents,etc. are charged, followed by carrying out polymerization according toconventional methods.

The monomer having an ethylenic double bond to which the method of thisinvention can be applied includes, for example, vinyl halides such asvinyl chloride; vinyl esters such as vinyl acetate and vinyl propionate;acrylic acid, methacrylic acid, and esters and salts thereof; maleicacid, fumaric acid, and esters and anhydrides thereof; and dienemonomers such as butadiene, chloroprene and isoprene; aromatic vinylcompounds such as styrene; as well as acrylonitrile, halogenatedvinylidenes, and vinyl ethers.

There are no particular limitations on the type of polymerization towhich the method of this invention can be applied. The present inventionis effective in any types of polymerization such as suspensionpolymerization, emulsion polymerization, solution polymerization, bulkpolymerization, and gas phase polymerization. Particularly, the presentmethod is suitable to polymerizations in an aqueous medium such assuspension or emulsion polymerization.

Specifically, in the case of suspension polymerization and emulsionpolymerization, polymerization is generally performed as follows, forinstance.

First, water and a dispersing agent are charged into a polymerizationvessel, and thereafter a polymerization initiator is charged.Subsequently, the inside of the polymerization vessel is evacuated to apressure of from about 0.1 to about 760 mmHg, and a monomer is thencharged (whereupon the pressure inside the polymerization vessel usuallybecomes from 0.5 to 30 kgf/cm².G). Then, the polymerization is normallycarried out at a temperature of from 30° to 150° C. During thepolymerization, one or more of water, a dispersing agent and apolymerization initiator may be added, if necessary. Reactiontemperature during the polymerization is different depending on the kindof monomer to be polymerized. For example, in the case of polymerizingvinyl chloride, polymerization may be carried out at 30° to 80° C.; inthe case of polymerizing styrene, polymerization may be carried out at50° to 150° C. The polymerization may be judged to be completed when thepressure inside the polymerization vessel falls to from about 0 to 7kgf/cm². G or when cooling water which passes through a jacket providedaround the polymerization vessel indicates almost the same temperatureat the inlet where it is charged and at the outlet where it isdischarged (i.e., when liberation of heat due to polymerization reactionhas been completed). The water, dispersing agent and polymerizationinitiator charged for the polymerization are used in amounts of about 20to 500 parts by weight, about 0.01 to 30 parts by weight, and about 0.01to parts by weight, respectively, per 100 parts by weight of themonomer.

In the case of solution polymerization, an organic solution such astoluene, xylene, pyridine and the like is used as a polymerizationmedium in place of water. The dispersing agent is optionally used. Theother conditions are generally the same as those described forsuspension and emulsion polymerizations.

In the case of bulk polymerization, after the inside of a polymerizationvessel is evacuated to a pressure of from about 0.01 mmHg to about 760mmHg, a monomer and a polymerization initiator are charged, and thenpolymerization is carried out at a temperature of from -10° C. to 250°C. For example, in the case of polymerizing vinyl chloride,polymerization is carried out at a temperature of from 30° C. to 80° C.;and in the case of polymerizing styrene, polymerization may be carriedout at 50° C. 150° C.

The present invention is effective in preventing polymer scale fromdepositing, independent of materials constituting the inner wall, etc.of a polymerization vessel. For example, this invention is effective inpreventing polymer scale from depositing in polymerization vessels madeof a stainless steel or other steels or vessels lined with glass.

Any additive materials that have been added in a polymerization systemcan be used without any limitation. More specifically, the method ofthis invention can effectively prevent polymer scale from depositing,even in polymerization systems containing the following additives: forexample, polymerization initiators such as t-butyl peroxyneodecanoate,bis (2-ethylhexyl) peroxydicarbonate, 3,5,5-trimethylhexanoyl peroxide,α-cumyl peroxyneodecanoate, cumene hydroperoxide, cyclohexanoneperoxide, t-butyl peroxypivalate, bis (2-ethylhexyl) peroxydicarbonate,benzoyl peroxide, lauroyl peroxide, 2,4-dichlorobenzoyl peroxide,diisopropyl peroxydicarbonate, α,α'-azobisisobutyronitrile,α,α'-azobis-2,4-dimethylvaleronitrile, potassium peroxodisulfate,ammonium peroxodisulfate, p-methane hydroperoxide; suspension agentscomprised of natural or synthetic polymeric compounds such as partiallysaponified polyvinyl alcohols, polyacrylic acids, vinyl acetate/maleicanhydride copolymer, cellulose derivatives such as hydroxypropylmethylcellulose, and gelatin; solid dispersing agents such as calciumphosphate and hydroxyapatite; nonionic emulsifying agents such assorbitan monolaurate, sorbitan trioleate and polyoxyethylene alkylether; anionic emulsifying agents such as sodium lauryl sulfate, sodiumalkylbenzenesulfonates such as sodium dodecylbenzenesulfonate and sodiumdioctylsulfosuccinate; fillers such as calcium carbonate and titaniumoxide; stabilizers such as tribasic lead sulfate, calcium stearate,dibutylthin dilaurate and dioctyltin mercaptide; lubricants such as ricewax, stearic acid and cetyl alcohol; plasticizers such as DOP and DBP;chain transfer agents such as trichloroethylene and mercaptans asexemplified by t-dodecyl mercaptans; and pH adjusters.

Addition to polymerization system

The polymer scale preventive agent of the present invention may be addedinto a polymerization medium in addition to the formation of thecoating, so that the scale preventing effect is further improved. Theamount of the polymer scale preventive agent to be added into thepolymerization medium, preferably ranges from about 10 ppm to 1,000 ppmbased on the whole weight of the monomer charged. The addition should beconducted so that it may not affect the quality of polymeric product tobe obtained with respect to fish eyes, bulk density, particle sizedistribution, etc.

EXAMPLES

The present invention is now described in detail by way of workingexamples and comparative examples. In each of the tables below,Experiments of Nos. marked with * are comparative examples, and theother Experiments working examples of the present invention. Chitosansused as the component (B) in Examples 1 and 2 below are those describedin Table 1.

                  TABLE 1                                                         ______________________________________                                                             Deacetylization                                          Chitosan.sup.(3)                                                                         Viscosity.sup.(1)                                                                       degree.sup.(2)                                                                            Manufacturer                                 ______________________________________                                        Chitosan (CHL)                                                                           100 cP or 80.0% or more                                                                             Yaizu                                                   more                  Suisankagaku                                                                  Kogyo K.K.                                   Chitosan (PSH)                                                                           100 cP or 80.0% or more                                                                             Yaizu                                                   less                  Suisankagaku                                                                  Kogyo K.K.                                   Chitosan (PSL)                                                                           100 cP or 80.0% or more                                                                             Yaizu                                                   less                  Suisankagaku                                                                  Kogyo K.K.                                   Chitosan (90M)                                                                           100 to    85.0 to     Wako Junyaku                                            300 cP    94.9%       Kogyo K.K.                                   Chitosan (100L)                                                                          30 to     99.0% or more                                                                             Wako Junyaku                                            100 cP                Kogyo K.K.                                   Chitosan (70H)                                                                           300 to    65.0 to     Wako Junyaku                                            500 cP    79.4%       Kogyo K.K.                                   Chitosan (80H)                                                                           300 to    75.0% to    Wako Junyaku                                            500 cP    84.9%       Kogyo K.K.                                   ______________________________________                                         Remarks:                                                                      .sup.(1) Viscosity: Measured at 20° C. with a Btype viscometer for     a 0.5 wt. % chitosan solution which was prepared by dissolving a chitosan     in an aqueous 0.5 wt. % acetic acid solution.                                 .sup.(2) Deacetylization degree: Measured by the PVSK colloid solution        titration method.                                                             .sup.(3) Tradenames are indicated in parentheses.                        

EXAMPLE 1

polymerization was carried out in the following manner using apolymerization vessel with an inner capacity of 1,000 liters and havinga stirrer.

In each experiment, first, a component (A) (N-substitutedleucophenothiazine), a component (B) (water-soluble basicpolysaccharide) were dissolved in a solvent so that the totalconcentration thereof might become the value given in Table 2, prepare acoating liquid. The coating liquid was applied to the inner wall andother parts with which a monomer comes into contact including thestirring shaft, stirring blades and baffles, followed by drying underheating at 40° C. for 15 min. to form a coating, which was then washedwith water.

In preparation of the coating liquids containing a water-soluble basicpolysaccharide, the water-soluble polysaccharide was dissolved in anaqueous ascorbic acid solution to form a polysaccharide solution, whichwas then diluted with methanol and the diluted solution was mixed with acomponent (A) dissolved in a solvent.

Experiment of No. 101 is a comparative example in which no coatingliquid was applied, and Nos. 102 and 103 are comparative examples inwhich coating liquids that contained either the component (A) or (B).

The N-substituted leucophenothiazine (A), the kind of the water-solublebasic polysaccharide (B), the total concentration of the components (A)and (B), the weight ratio of (A)/(B), and the solvent used in eachexperiment are given in Table 2.

Subsequently, in the polymerization vessel in which a coating had beenformed by the coating operation as above, were charged 400 kg of water,200 kg of vinyl chloride, 250 g of a partially saponified polyvinylalcohol, 25 g of hydroxypropylmethyl cellulose and 75 g of diisopropylperoxydicarbonate. Then, polymerization was carried out at 57° C. withstirring for 6 hours. After the completion of the polymerization, theamount of polymer scale depositing on the inner wall of thepolymerization vessel and the whiteness or initial coloration of thepolymer obtained were measured according to the following.

The scale depositing on the inner wall surface in an area of 10 cmsquare were scraped off with a stainless steel spatula as completely aspossible to be confirmed with naked eyes, and then the scraped scale wasweighted on a balance. Thereafter, the amount of the deposited scale perarea of 1 m² was obtained by multiplying the measured value by 100.

Measurement of initial coloration of polymer

A hundred parts by weight of a polymer, one part by weight of a tinlaurate stabilizing agent (trade name: TS-101, product of AkishimaChemical Co.) and 0.5 part by weight of a cadmium stabilizing agent(trade name: C-100 J, product of Katsuta Kako Co.), and 50 parts byweight of a plasticizer DOP were kneaded at 160° C. for 5 min. with atwin roll mill, and then formed into a sheet 1 mm thick. Subsequently,this sheet was placed in a mold measuring 4 cm×4 cm×1.5 cm (thickness),and molded under heating at 160° C. and under a pressure of 65 to 70kgf/cm² to prepare a test specimen. This test specimen was measured forluminosity index L in the Hunter's color difference equation describedin JIS Z 8730 (1980). Initial coloration is evaluated to be morefavorable with increase in L value.

The L value was determined as follows.

The stimulus value Y of XYZ color system was determined according to thephotoelectric tristimulus colorimetry using the standard light C, aphotoelectric colorimeter (Color measuring color difference meter ModelZ-1001DP, product of Nippon Denshoku Kogyo K.K.) in accordance with JISZ 8722. As the geometric condition for illumination and beingilluminated, the condition d defined in section 4.3.1 of JIS Z 8722 wasadopted. Next, L was calculated based on the equation: L=10Y1/2described in JIS Z 8730(1980).

The results are given in Table 2.

                                      TABLE 2                                     __________________________________________________________________________    Coating liquid                                                                                                    Total                                                                         conc. of            Amount                Exp.                        (B) Basic                                                                             (A) + (B)                                                                           Wt. ratio                                                                          Solvent  of scale              No.                                                                              (A) N-Substituted leucophnothiazine                                                                    polysaccharide                                                                        (wt. %)                                                                             (A)/(B)                                                                            (wt. ratio)                                                                            (g/m.sup.2)                                                                        L                __________________________________________________________________________    101*                                                                             --                       --      --    --   --       1300 73               102*                                                                             --                       Chitosan (PSH)                                                                        0.2    0/100                                                                             Methanol/Water                                                                          15  73                                                              (75/25)                        103* 104 105 106                                                                  ##STR6##                -- Chitosan (PSH) Chitosan (100L) Chitosan                                    (70H)   0.05 0.05 0.05 0.1                                                                  100/0 100/400 100/900 100/1900                                                     Methanol Methanol/Water                                                       (90/10) Methanol/Water                                                        (90/10) Methanol/Water                                                        (70/30)    8  73 72 72 71      107* 108 109 110                                                                  ##STR7##                -- Chitosan (PSL) Chitosan (90L) Chitosan                                     (70H)   0.05 0.05 0.1 0.2                                                                   100/0 100/230 100/900 100/900                                                      Methanol/Water (30/70)                                                        Methanol/Water (50/50)                                                        Methanol/Water (70/30)                                                        Methanol/Water (70/30)                                                                   9  73 71 72         __________________________________________________________________________                                                                 72                *Comparative examples                                                    

EXAMPLE 2

In each experiment, the coating procedure of Example 1 was repeated fora stainless steel polymerization vessel having an inner capacity of 20liters and equipped with a stirrer, except that a coating liquid inwhich the N-substituted leucophenothiazine (A), the water-soluble basicpolysaccharide (B), the total concentration of the components (A)+(B),the weight ratio of (A)/(B), and the solvent were as given in Table 3,was used. Experiment of No. 201 is a comparative experiment in which nocoating liquid was applied, and Experiment Nos. 202 and 203 arecomparative experiments in which coating liquids that contained eitherthe components (A) or (B) were used.

In preparation of the coating liquids containing a water-soluble basicpolysaccharide, the water-soluble polysaccharide was dissolved in anaqueous glycollic acid solution to form a polysaccharide solution, whichwas then diluted with methanol and the diluted solution was mixed with acomponent (A) dissolved in a solvent.

In the polymerization vessel in which the coating was thus formed, werecharged 9 kg of water, 225 g of sodium dodecylbenzenesulfonate, 12 g oft-dodecyl mercaptan, and 13 g of potassium peroxodisulfate. After theinner atmosphere was replaced with a nitrogen gas, 1.3 kg of styrene and3.8 kg of butadiene were charged, followed by polymerization at 50° C.for 20 hours.

After completion of the polymerization, the amount of polymer scaledepositing on the inner wall surface was measured.

The results are given in Table 3.

                                      TABLE 3                                     __________________________________________________________________________    Coating liquid                                                                                                      Total                                                                         conc. of            Amount              Exp.                         (B) Basic                                                                              (A) + (B)                                                                           Wt. ratio                                                                          Solvent  of scale            No.                                                                              (A) N-Substituted leucophnothiazine                                                                     polysaccharide                                                                         (wt. %)                                                                             (A)/(B)                                                                            (wt. ratio)                                                                            (g/m.sup.2)         __________________________________________________________________________    201*                                                                             --                        --       --    --   --       400                 202*                                                                             --                        Chitosan (70H)                                                                         0.2    0/100                                                                             Methanol/Water                                                                          20                                                                  (75/25)                      203* 204 205 206                                                                  ##STR8##                 -- Chitosan (70H) Chitosan (80H) Chitosan                                     (PSH)    0.2 0.1 0.1 0.1                                                                      0/100 100/25 100/230                                                         100/100                                                                            Methanol Methanol/Water                                                       (80/20) Methanol/Water                                                        (90/10) Methanol/Water                                                        (90/20)   8  4  4            __________________________________________________________________________                                                              3                    *Comparative examples                                                    

We claim:
 1. A process of producing a polymer by polymerization of amonomer having an ethylenically unsaturated double bond in apolymerization vessel, comprising the step of carrying out saidpolymerization in a polymerization vessel having on its inner wallsurfaces a coating for preventing polymer scale deposition, wherein thecoating comprises:a solution or dispersion of (A) an N-substitutedleucophenothiazine having the formula (I): ##STR9## wherein Z is acarbonyl group or a sulfonyl group, R¹ and R² may be the same ordifferent and each represent a hydrogen atom, a hydroxyl group or agroup having the formula --N(R⁴) (R⁵) where R⁴ and R⁵ may be the same ordifferent and each represent a hydrogen atom, an alkyl group or a formylgroup, and R³ is a hydrogen atom, halogen atom, alkyl group, haloalkylgroup, alkoxy group, aryl group or a group having the formula: --N(R⁶)(R⁷) where R⁶ may be the same or different and each represent a hydrogenatom or an alkyl group, and (B) a water-soluble basic polysaccharidewhich is a chitosan, water-soluble chitosan derivative,polygalactosamine, water-soluble polygalactosamine derivative orwater-soluble chitin, in a solvent.
 2. The process according to claim 1,wherein said polymerization is carried out as suspension polymerization,emulsion polymerization, solution polymerization, bulk polymerization,or gas phase polymerization.
 3. The process according to claim 1,wherein said monomer is selected from the group consisting of vinylhalides; vinyl esters; acrylic acid, methacrylic acid and esters andsalts thereof; maleic acid and fumaric acid, and esters and anhydridesthereof; diene monomers; aromatic vinyl compounds; acrylonitrile;halogenated vinylidenes; and vinyl ethers.